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<html><head><title>Using rn</title></head><body><h1><a name=top>rn</a></h1>rn provides a more or less convenient wrapper aroundtwo very efficient notification mechanisms, sigio and epoll.See <a href="http://www.kegel.com/c10k.html">www.kegel.com/c10k.html</a>for a description of thesetwo mechanisms. Basically, they are standard Linux replacementsfor poll that are much more efficient.The right one to use is almost always epoll; sigio is only a fallback,as it's less efficient.<p>The odd thing about rn is that you have to tell it the maximumnumber of file descriptors you expect to have to use,and (if you want to work with sigio) you have to tell itwhich realtime signal to use to deliver its notifications.<p>The epoll library must be installed before you can build rn.<h2><a name=use>Using rn</a></h2>The api is fairly simple; see <a href="rn_test.c">rn_test.c</a> for an example.<p>Here are the steps to add rn support to a program currently using poll():<ul><li>In source code that currently uses poll(), add the line<pre>#include <rn.h></pre>to get access to rn.<li> Link your program with -lrn. You *might* also have to link with -lepoll,but not if you're using glibc-2.3.2 or later.<li> In main(), or somewhere near startup, create an object of type rn_t, and call rn_init() and rn_setSignum() on it. e.g.<pre>rn_t rns;if (rn_init(&rns, 128)) { printf("FAIL: rn_init failed \n"); exit(1);}if (rn_setSignum(&rns, SIGRTMIN)) { printf("FAIL: rn_setSignum failed \n"); exit(1);}</pre>The second argument to rn_init() should be the highest file descriptoryou expect to ever see in your program, or roughly the numberof sockets you expect to have open at any one time.<p>The second argument to rn_setSignum() is the realtime signal rn should useinternally. Usually SIGRTMIN is fine.<li> Whenever you create a socket fd, add it to the rn as follows:<pre>err = rn_prepare_fd_for_add(fd, getpid());if (err) { printf("FAIL: rn_prepare_fd_for_add failed, errno %d\n", err); exit(1);}err = rn_add(&rns, fd, my_callback, NULL);if (err) { printf("FAIL: rn_add failed, errno %d\n", err); exit(1);}</pre>The third argument to rn_add() is your readiness event handler function; it is calledwhenever that socket becomes ready for I/O.The fourth argument to rn_add() is for your use; it is a context pointer that will bepassed back when your readiness event handler is called. You can use it to holda pointer to the object associated with that socket. (If there is demand,I may add a C++ wrapper for rn so C++ programmers could simply give an objectpointer here, and inherit from class rnClient, then override its virtualreadiness event handler method.)<li> Whenever you close a socket fd, remove it from the rn as follows:<pre>rn_del(&fns, fd);</pre><li> Replace the call to poll() in your program with a call to rn_waitAndDispatchEvents():<pre>rn_waitAndDispatchEvents(&rns, timeout_milliseconds);</pre>The second argument to rn_waitAndDispatchEvents is the timeout inmilliseconds; the call will sleep until some sockets areready for I/O, but no longer than timeout_milliseconds.<li> Replace the code after poll() that looks at the ready fd array with an event handler callback function. Basically, rn_waitAndDispatchEvents willlook at the ready fd array for you, and call the event handler functionyou specified in rn_add() whenever the socket you specified in rn_add() becomesready for something.<li> (The hardest part of all:) never, ever return from your event handler functionwithout either "using up" the readiness status of the socket, or storing it forlater action. In the simplest case of reading from a socket, you must continuecalling read() on the socket until read() returns a partial buffer or returns-1 and sets errno to EWOULDBLOCK. (Or until you close the socket.)If you fail to read all the bytes waiting to be read, your event handlermight never be called again, and your state machine will jam.</ul><p><h2><a name=test>Unit test</a></h2>The rn library comes with a test program which doubles as a demo.The test program is unfortunately not standalone -- it relies onthe 'chargen' tcp server, which you may have to enable by editing /etc/inetd.conf, then restarting inetd.<p>Here's what a successful run looks like:<pre># ./rn_testfn: revents 4rn_POLLOUTfn: revents 5fn: read returns 1024, errno 11... (repeats 62 times)fn: read returns 1024, errno 11fn: read returns 977, errno 11Read 66513 bytesPASS</pre>If you're debugging a program that uses rn, you may wish to rebuildrn with dprints enabled. To do this, uncomment the lines<pre>/* #define dprint_ENABLED *//* #define dprint_TRACE_ENABLED */</pre>in rn_dprint.h, and rebuild and reinstall rn.With dprint enabled, a successful run looks like this:<pre># ./rn_test-469985671:47:rn_sys_epoll.c:rn_sys_epoll_init init()-469985652:150:rn_sys_epoll.c:rn_sys_epoll_add add(4, 0x10000954, (nil)) this->m_fds_used 1-469985651:198:rn_sys_epoll.c:rn_sys_epoll_waitAndDispatchEvents Calling epoll...-469985651:200:rn_sys_epoll.c:rn_sys_epoll_waitAndDispatchEvents epoll returns 1 fds. errno: 11-469985651:213:rn_sys_epoll.c:rn_sys_epoll_waitAndDispatchEvents fd 4, revents 4fn: revents 4rn_POLLOUT-469985651:198:rn_sys_epoll.c:rn_sys_epoll_waitAndDispatchEvents Calling epoll...-469985638:200:rn_sys_epoll.c:rn_sys_epoll_waitAndDispatchEvents epoll returns 1 fds. errno: 11-469985638:213:rn_sys_epoll.c:rn_sys_epoll_waitAndDispatchEvents fd 4, revents 5fn: revents 5fn: read returns 1024, errno 11... (62 lines like the one above)fn: read returns 1024, errno 11fn: read returns 118, errno 11Read 65654 bytes-469985628:160:rn_sys_epoll.c:rn_sys_epoll_del del(fd 4)PASS</pre><hr><i>Last change: 10 Nov 2003<br>Portions Copyright 2002 Dan Kegel<br>Portions Copyright 2003 Ixia Communications<br>Licensed under the LGPL<br>[<a href="http://www.kegel.com/rn/">Return to kegel.com/rn</a>]</i></body></html>?? 快捷鍵說明
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